May 30, 1918] 



NATURE 



253 



T 



two photographs taken by Dr. Lunt at the Cape Ob- 



- rvatory in October of" last year, and data for the 



imputation of a provisional orbit were provided by 



ilieen plates taken later (Astrophy steal journal, 



\ol, xlvii., p. 134). The magnitude of the star is 



528, and the spectrum of type K. The semi-ampli- 



lude of the velocity curve is 2275 km. /sec, and the 



system is approaching with a velocity of 30 km. /sec. 



i.latively to the sun, or receding at 7-3 km. /sec. when 



!!■ component of the solar motion is eliminated. The 



ir is of special interest, inasmuch as the period is 



"ly. 1325 days, whereas Campbell found no spectro- 



-I opic binaries of the later types G, K, and M having 



|)« liods less than twenty days. 



THE TOTAL SOLAR ECLIPSE 

 OF JUNE 8, 1918. 

 HE "Eclipse Number" of Popular Astronomy 

 (vol. xxvi.. No. 5, May) gives special prominence 

 to a number of articles on the approaching total eclipse 

 of the sun visible in the United States. Prof. H. C. 

 Wilson gives a general account of eclipse phenomena 

 and of the circumstances of the eclipse of June 5, to 

 which is appended a series of letters indicating the plans 

 of leading astronomers for observing the eclipse. The 

 shadow first strikes the earth in the Pacific south of 

 Japan, then passes north-westward, and reaches its 

 highest latitude about 500 miles south of the Alaskan 

 coast in long. 152*^ W. ; on its landw^ard course it 

 passes from the western coast of Washington by way 

 of Denver to Florida, the duration of totality on the 

 central line gradually diminishing from 121 to 50 sec. 

 Quite Si large number of American astronomers are 

 too fully occupied with war-work to undertake ob- 

 servations, but several well-equipped parties will 

 occupy stations along the track. Ample provision 

 appears to have been made for direct photographs of 

 the corona on large and small scales, as well as for 

 spectroscopic observations, and some of the observers 

 will make special efforts to obtain photographs suit- 

 able for testing the deflection of rays of light from 

 stars near the sun which is predicted by Einstein's 

 theory of relativity. Prof. Hale will be in Wyoming 

 with a party from the Mt. Wilson Observatory, and 

 will attempt to determine the rotation of the corona 

 • from displacement^; of the green coronal line, besides 

 obtaining photographs for studies of the chromo- 

 spheric spectrum at different levels. Prof. CampbeJl's 

 programme is somewhat restricted by the delay in 

 the return of the instruments employed by him in 

 Russia in 1914, but some instruments are available 

 for photographs of the corona and of its spectrum. 



The observations proposed by Prof. Abbot include 

 measures of the brightness of the sky and of the 

 outgoing radiation before, during, and after the 

 eclipse. Prof. Stebbins will endeavour to secure photo- 

 metric rneasures of the corona by means of potassium 

 and rubidium photo-electric cells. A large party from 

 the U.S. ?7aval Observatory will be located at Baker, 

 Oregon, and in addition to many other observations, 

 will attempt to extend the spectroscopic observations 

 into the extreme red by the use of plates stained with 

 dicyanin. Profs. Frost and Barnard have also pre- 

 pared , an extensive programme of photographs of the 

 corona and its spectrum at Green River, Wvoming. 

 In a separate article Prof. Frost directs attention to 

 the valuable observations of the chromospheric spec- 

 trum which are possible at places within 200 miles of 

 the eclipse track, as indicated by Newall and. Fowler 

 in 1912. 



On account of the war, it is not e.xpected that 

 lliere will be any expeditions from foreign countries 

 1.1 (tbserve this eclipse. 



NO. 2535, VOL. lOl] 



DIURNAL VARIATION OF ATMOSPHERIC 



PRESSURE. 

 'T* HE effect of geographicjtl latitude on the semi- 



■■■ diurnal wave of atmospheric pressure is fairlv 

 regular and well marked, but the variation of the 

 diurnal wave has attracted less attention since Angpt 

 in 1887, and also Hann, showed conclusively its de- 

 pendence on secondary local conditions. Three 

 Japanese investigators from the Geophysical Seminary 

 of the Physical Institute, Tokyo, contribute an account^ 

 of a preliminary attempt to trace more detinitely the 

 mechanism of these local influences, one of the most 

 obvious of which, uiuler the name of " continentality," 

 has recently been attracting the attention of Mr. 

 C. IC. P. Brooks in this country- in connection with 

 climate, and with a purely geographical theory of- the 

 Ice age. 



The ^ementary definition of continentality as the 

 percentage of land in a circle of definite size (say 10° 

 radius) surrounding the station is clearly insufficient, 

 so much depending upon the orientation and shape of 

 the coast line or lines that the form of the fujnction is 

 bound to be complicated. The Japanese autKors soon 

 come to the conclusion that it is not linear, and are 

 constrained to make a series of simplifying assump- 

 tions in order to reach a workable hypothesis. The 

 assumptions are no more probable than those of the 

 early days of the theory of tides, with which the pre- 

 sent problem has obvious analogies. 



With these limitations the authors appear to account 

 for such features as the variation with longitude, the 

 inversion of phase near the poles, and the minimum 

 amplitude near the coast, but a general solution of tlie 

 problem has evidently not yet been reached. They 

 indicate the lines on which they propose to continue 

 the investigation, and conclude with a representative 

 set of daily variation curves for ten. British observa- 

 tories, showing considerable dissimilarity, those of 

 Oxford and Aberdeen, for instance, being almost, the 

 converse of each other. A systematic series of stations 

 within the Empire, chosen with special reference to 

 the elucidation of this problem, mav well form part 

 of the programme of co-ordinated' British Empire 

 meteorology so strongly advocated bv Major Lyons 

 in his presidential address to the Royal Meteorological 

 Society. 



The barometric variations dealt with in the 

 above paper, as generally studied, are natur- 

 ally to be regarded as vertical oscillations of 

 the free atmosphere, though there is a pos- 

 sible difficulty in the differentiation between statical 

 and dynamical pressure, when an ascending or descend- 

 ing current is in question. But there is also a very 

 decided horizontal oscillation or motion of the .free 

 atmosphere, and this has begun to attract attention 

 since the use of pilot balloons has provided more in- 

 formation about the direction of the wind at different 

 heights than can be inferred from the motion of clouds. 

 A paper from Batavia ^ has appeared in the Proceedings 

 of the Royal .Academy of Amsterdam dealing with the 

 semi-diurnal variation of this motion. 



There is a good deal of uncertainty about the inves- 

 tigation, even in a favourable place like Batavia. where 

 atmospheric conditions are as a rule very quiet and 

 steady. Observations were made not only' at Batavia, 

 but also at a neighbouring mountain station of 3000 

 metres elevation, as well as from a small coral island, 

 to eliminate the land-effect. Single observations are 



, ' J^P") Diumal Variation of Barometric Pressure." By T. Terada, 

 M. Kiiiti, and T. Tukamoto. Journal of the College of Science, Imperial 

 University of Tokyo, vol. xli., art. i (November ao. 1917). 



2 " The Semi-diurnal Horizontal Oscillation of the Free Atmosphere up 

 to 10 km. above Sea-leve! Dediicrd from Pilot-Balloon Observations at 

 Batatvia." By W. van Bemmelen and J. Boerema. Proceedings Ro>-al 

 Acad. Amsterdam, vol, xx*, pp. ii9-;^5-(- plate. 



